Fix typos in unittest documentation (GH-24194)

* addCleanupClass  -> addClassCleanup
* doCleanupsClass -> doClassCleanups
(cherry picked from commit e0e398e)

Co-authored-by: Conchylicultor <[email protected]>

Author: miss-islington

Doc/library/unittest.rst

@@ -1477,11 +1477,11 @@ Test cases
       after :meth:`setUpClass` if :meth:`setUpClass` raises an exception.
 
       It is responsible for calling all the cleanup functions added by
-      :meth:`addCleanupClass`. If you need cleanup functions to be called
+      :meth:`addClassCleanup`. If you need cleanup functions to be called
       *prior* to :meth:`tearDownClass` then you can call
-      :meth:`doCleanupsClass` yourself.
+      :meth:`doClassCleanups` yourself.
 
-      :meth:`doCleanupsClass` pops methods off the stack of cleanup
+      :meth:`doClassCleanups` pops methods off the stack of cleanup
       functions one at a time, so it can be called at any time.
 
       .. versionadded:: 3.8